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LP5907UV-3.3EVM: which layout is best?

Andre Strul
Expert 1330 points

Part Number: LP5907UV-3.3EVM

Hi to all and thank you in advance for your support.

we would like to know which layout you recommend the most in a 4 layer PCB.

A / B or C ?  thank you !

  • 0
    TI__Guru 55940 points

    Hi Andre,

    It looks like you are using the SOT-23 package for your application.  Please note that we provide layout examples in our datasheets.  Below please find our recommendation from our datasheet.

    Please note that we recommend same layer connections for the input and output capacitors to the LDO in order to minimize inductance and resistance.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Expert 1330 points
    HI Ryan,
    we saw the layout in the datasheet, but we are asking a specific questions concerning our design.
    which one of the 3 choices would you recommend ?

    thanks for taking the time to reply.
    regards
    Andre
  • 0 in reply to Andre Strul
    TI__Guru 55940 points
    Hi Andre,

    I am assuming that your black dots represent vias on the GND plane. If so, your drawing B and C both indicate a same layer connection for the capacitors to the LDO. Either of those will be fine. Your drawing A does not show a same layer connection for the ground end of the output capacitor to the ground pin of the LDO.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Expert 1330 points
    Hello Ryan and thank you for the reply, we understand.

    One more question, please:
    Our GDN trace extends all the way under the LDO package. Any advantages doing that instead of a straight line ?

    Thanks again.
  • 0 in reply to Andre Strul
    TI__Guru 55940 points
    Hi Andre,

    Since LDOs are power dissipative products, we generally recommend having as much copper as possible to pull heat out of the LDO. Typically this is easiest to accomplish with a large GND plane. The advantage you will gain with additional GND copper is better thermal performance.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Expert 1330 points
    HI again Ryan,
    is it possible that ground layer under the LDO helps cancel magnetic fields (and thus noise) from positive rail ?
    thanks
    Andre
  • 0 in reply to Andre Strul
    TI__Guru 55940 points
    Hi Andre,

    Unfortunately the solid copper ground layer will not likely have too much effect on magnetic fields. The magnetic permeability of copper is rather low. Furthermore, magnetic fields can go around the board.

    Very Respectfully,
    Ryan